1. Field of the Invention
The present invention relates to an ultrasonic actuator which circulates traveling waves around the surface of a vibration block and which moves a movable member by the action of these traveling waves.
2. Description of the Related Art
In the prior art, as such a type of ultrasonic actuator, there has for example been disclosed a type described in U.S. Pat. No. 4,562,374. FIGS. 11 through 13 are figures illustrating an example of a prior art type ultrasonic actuator.
The ultrasonic actuator shown in FIG. 11 is constructed so as to have a vibration block 20 which is rod shaped and is bent around and joined to itself so that both of its surfaces are endless. A piezoelectric element 21 is fixedly contacted to a first portion of the surface of this vibration block 20, and further a plate shaped movable member 22 is kept in pressure contact with another portion of the surface of this vibration block 20. When the piezoelectric element 21 is driven so that vibrations are excited in it, bending vibrations are set up in the vibration block 20, and traveling waves are generated by these transverse vibrations, by which the movable member 22 is driven. Since the vibration block 20 is formed so as to be endless, these traveling waves set up in the vibration block 20 are recirculated in a non-terminating cycle within the vibration block 20.
The ultrasonic actuator shown in FIG. 12A is constructed so as to have two vibration blocks 30 and 31, both of which are rod shaped and the ends of which are connected together by two couplers 32 and 33. A piezoelectric element 34 is fixedly contacted to the surface of the one 30 of these vibration blocks, and further a plate shaped movable member 35 is kept in pressure contact with the surface of the other one 31 of these vibration blocks. When the piezoelectric element 34 is driven so that vibrations are excited in it, bending vibrations are set up in the vibration block 30, and traveling waves are generated by these bending vibrations which are transmitted to the other vibration block 31 via the coupler 32, by which the movable member 35 is driven. The traveling waves transmitted through the vibration block 31 return round to the vibration block 30 via the other coupler 33, and in this manner the traveling waves are recirculated in a non-terminating cycle.
With the ultrasonic actuator shown in FIG. 12B, instead of the couplers 32 and 33, the vibration blocks 30 and 31 are linked together by oscillators 36 and 37.
With the ultrasonic actuator shown in FIG. 13, two vibrators 41 and 42 are linked by couplers 43 and 44 to the vibration block 40 which is formed in a rod shape. When the vibrators 41 and 42 are driven so that vibrations are excited in them, bending vibrations are set up in the vibration block 40 via the couplers 43 and 44, and traveling waves are generated by these bending vibrations which move a movable member not shown in the figures so as to drive it. The traveling waves transmitted through the vibration block 40 are converted into electrical signals by a vibrator which is connected to the vibration block 40 but which is not shown in the figures, and this electrical signal is returned to the vibrators 41 and 43. In this manner the traveling waves are effectively recirculated in a non terminating cycle.
However, with the ones of these prior art types of ultrasonic actuator in which the vibration propagation path of the vibration block is made to be endless in order to return the traveling waves from the portion of the vibration block which drives the movable member to the portion thereof which generates the traveling waves, the problem arises that the overall dimensions of the ultrasonic actuator become great because the vibration propagation path is required to be long. On the other hand, with the ones of these prior art types of ultrasonic actuator in which the traveling waves are recirculated electrically, the problem arises that the cost is increased due to the construction of the ultrasonic actuator becoming more complicated.